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From: Tony Williams
Subject: Re: zero-power toggle circuit; was, how to master electronics
Date: Sat, 23 Nov 2002 23:34:00 +0000 (GMT)
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <3DDFAF13.email@example.com> <3DDFF582.firstname.lastname@example.org>
NNTP-Posting-Date: Sat, 23 Nov 2002 23:44:16 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article <3DDFF582.email@example.com>,
Fred Bloggs wrote:
> Right- that's always a problem- even for the paralleled 4049 but maybe
> not of this magnitude. In operation at the supply voltages you describe,
> the left inverter output should transition between the supply rails in
> under 50ns which means say at 15V the "shoot-through" region will be
> traversed in 50/3=17ns. I am not so sure those slow-poke 2N440x's will
> go from 0 to 60MPH in that time frame-as a matter of fact, the diffusion
> capacitance alone is 21nF at 500mA. So the crowbar will more likely be
> 1/10 of your estimate.
Hang on Fred, I've just noticed something......
Those 5.6k's etc is a quite a neat looking trick,
(worth remembering, especially for single ended o/p).
But at the end of the day those output transistors
are actually being driven as darlingtons. So the Vout
to the big external MOSFET will always go to no better
than a Vbe away from the rails. That circuit also has
no zero current state... it will always draw Vbe/5.6k.
In which case the transistors can just as well be
used as a normal pnp/npn emitter follower pair, which
will have the same Vout capability, but without the
Add a 4k7 between bases and emitters, so that (when
the transistors have finished their fast thrash) the
CMOS can push Vout fully to the rails (and shut down
both bipolar transistors).
Note to Win (just to make your day). I think the 4007A
*does* have the MOSFETs required to make the original
2-MOSFET RTL latch, plus the push-pull inverter for
driving an external MOSFET.
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